The interim report into the crash also says evidence indicates the top of the crane on The Tower, St George Wharf, was obscured by cloud and details the final exchange between the pilot and the air traffic controller.

Weather discussion

Matthew Wood, 39, of Sutton, south London, was killed as he was walking to work.

The Met Office said at the time of the crash the area was prone to widespread low cloud, poor visibility and patches of freezing fog.

Mr Barnes, 50, was flying from Redhill Aerodrome in Surrey to Elstree when the helicopter crashed into the crane and the wreckage fell into Wandsworth Road.

Helicopter pilot's last conversation

Mr Barnes had worked as a pilot on action films

Poor weather conditions at Elstree meant Capt Pete Barnes asked to route back to Redhill Aerodrome via the London Eye.

07:55 The helicopter was put under radar control as it entered the London CTR.

07:56 pilot: "Rocket 2, is Battersea open do you know?"

After being told London Heliport was open the pilot said: "If I could head to Battersea that would be very useful."

Air traffic control (ATC) responded: "I'll just have a chat with them and see what the cloud is looking like."

07:57 The helicopter was at right angles to the London Eye at 1,500 ft.

Pilot: "Rocket 2, I can actually see Vauxhall, if I could maybe head down to H3... H4 sorry."

ATC: "Rocket 2, you can hold on the river for the minute between Vauxhall and Westminster bridges and I'll call you back."

The helicopter passed Westminster Bridge and began to descend and at 07:58 was approaching the north side of the river.

ATC: "Rocket 2 Battersea are just trying to find out if they can accept the diversion, you can make it quite a wide hold, and you can go as far as London Bridge."

The total height from the ground to the top of the crane's jib was 719 ft (219m).

About 500kg of jet fuel was on board at the time.

Witness and CCTV evidence indicate the top of the crane and the top of the building to which it was attached were obscured by cloud at the time of impact.

The fuel ignited at the point of impact with the ground.

The main rotor head, gearbox and a section of one of the four rotor blades from the helicopter landed in the loading bay of the nearby New Covent Garden Flower Market where it hit a delivery van.

The AAIB was notified of the crash at 08:20.

'Extremely hard'

In the report, it said it would "conduct a detailed inspection of recovered wreckage and helicopter maintenance documents, and an analysis of weather conditions".

It added: "The investigation will also examine the conduct of this flight, regulation of flights over London, planning guidance and regulations relevant to development around aerodromes, and the lighting of obstacles."

Mist shrouds the damaged crane on The Tower on the day of the crash

Aviation expert David Learmont from Flight International magazine said the pilot faced a very difficult task in changing course to land at Battersea.

"It was extremely hard as he couldn't go up much because of Heathrow's approach, and he couldn't go down because of the high buildings.

"He wasn't doing a 180 degree turn for fun.

"He was carrying out a turn to the right and that is a demanding manoeuvre in conditions where visibility is limited.

"He also had to look everywhere at the same time; down where the Thames is as he was navigating by that to get to Battersea; sideways into the turn and he also had to turn his eyes downward to retune the radio to Battersea. He had a lot on his hands."

Mr Learmont said what the report did not say was what the visibility was like at the height Mr Barnes was flying.

He added that radar can be used by air traffic control to direct helicopters to avoid objects however that can involve a very big detour.

Mr Learmont said Mr Barnes was navigating visually so he either did not see the crane, or it could not be seen.